If you are wanting to make some nice looking 15mm trees really cheaply and easily then give plastic flowers a try! They are some of the best readymade armatures you will find for making trees. The following are three more flower types that work very well at 15mm scale.
The first ones were made using these really ugly cheap plastic flowers. Each stem only had a few clusters on it, but we got them on sale at a great price.
The flowers were plucked off of the stems.
They were then hot glued down to a heavy washer, and painted with a paint that “bonds to plastic”. Because the flowers were very knobby, and square, we used an intermediary flock. Using static grass as the intermediary flock changed the flower to something a little les distinct in shape. Once it had dried another layer of fine flock was then added to give it the final color and shape.
This next flower had lots of them on each stem, but they were each very slim.
A few plants gave us a large pile of usable material.
Glue to the base, paint, and then flock. These are perfect to use as decorative little trees to line roads with or as filler to add bulk to a forest.
This plant is sold as a decorative ivy or garland.
Each individual piece is somewhat flat, so they must be used in groupings to get the three dimensional look that is needed for a tree.
If you are trying to model a thicket or a tree with multiple slim trunks, then this is an excellent plant to use.